Manning is the prime suspect in the WikiLeaks incident, according to military officials

Washington (CNN) -- The Army private charged with leaking an airstrike video and downloading documents remained in solitary confinement Saturday.

Military officials told CNN that Pfc. Bradley Manning is also the prime suspect in the latest leak of documents to the WikiLeaks website.

Manning was routinely processed Thursday at the Quantico detention facility, a military spokesman said Friday.

Manning arrived at 9:30 p.m. Thursday and was given a physical exam and medical screenings, according to Lt. Col. Rob Manning (not related) of the Military District of Washington. The suspect is in solitary confinement and is being observed in accordance with normal operating procedures, the spokesman said.

Manning's legal future is complex. He has already been charged with leaking a 2007 airstrike video and downloading documents from classified military systems. And he is suspected in the latest leak of thousands of Afghanistan field reports to the Wikileaks.org website.

Julian Assange, WikiLeaks founder, has declined to say where his whistle-blower website got about 91,000 U.S. documents about the war. About 76,000 of them were posted on the site Sunday in what has been called the biggest leak since the Pentagon Papers about the Vietnam War.

The documents are divided into more than 100 categories and touch on everything from the hunt for al Qaeda leader Osama bin Laden to Afghan civilian deaths resulting from U.S. military actions. Thousands of pages of reports document attacks on U.S. troops and their responses, relations between Americans in the field and their Afghan allies, intramural squabbles among Afghan civilians and security forces, and concerns about neighboring Pakistan's ties to the Taliban.

Manning could go before a military judge in August in Washington, but given the complexity of the case it could likely be delayed, the military official said.Investigators are gathering evidence on the initial charges, which they will present to a military judge who will approve a court martial if the case adds up, the military official said.

Manning, the military spokesman, said no hearing dates have been set, as the uniformed code of military justice is a "very deliberate process." All parties are working to assure that the private's rights are protected, he added.

Requests for comment from Manning's attorney, Capt. Paul Bouchard, were not returned.

The investigation has also been expanded, with the help of the FBI, in the wake of the new leak. The FBI is assisting the Defense Department in the Wikileaks investigation of Manning but remain tight-lipped on what or who they're looking at or interviewing. On background, one FBI official acknowledges the Bureau is involved in the investigation of potential civilian co-conspirators who may have played a role in the leaking of the classified material.

The FBI official says that while Manning would appear in a military court, any civilian, whether a government employee or not and regardless of the charges, would be charged in a U.S. District Court

The official on background did refer to FBI involvement in past "espionage" cases, a signal the FBI is considering whether particular espionage statutes may be applicable in any potential prosecutions of civilians who played a role in the leak.

The official gave no indication whether WikiLeaks or Julian Assange are under investigation.